PD CEN TS 16835 — Molecular In Vitro Diagnostic Examinations Specifications for Pre-examination Processes for Venous Whole Blood Standard Series

🩸 PD CEN TS 16835 is the British Standards Institution (BSI) Published Document implementing the European Technical Specification CEN/TS 16835, covering pre-examination processes for venous whole-blood samples in molecular in vitro diagnostics (IVD). Prepared by the UK technical committee CH/212 “IVDs” and classified under ICS 11.100.10 and 11.100.30 (in vitro diagnostic analytes and specimen pre-examination), the series sets standardised requirements for extracting and testing cellular RNA, genomic DNA, and plasma cell-free DNA (cfDNA) — a key underpinning of liquid biopsy, haematological molecular testing, prenatal screening, and hereditary-disease diagnostics.

💡 Once blood leaves the body, its cellular components and free nucleic acids change rapidly: RNA can be induced, leucocytes can lyse and release DNA, and cfDNA can be degraded. Pre-examination timing, temperature, and anticoagulant choice directly determine the reliability of downstream molecular assays.

1. Series Structure and Overall Framework 📌

The PD CEN TS 16835 series consists of 3 parts, each targeting one analyte class from venous whole blood: cellular RNA, genomic DNA, and plasma cell-free DNA. All three share general considerations and terminology, with part-specific requirements for each analyte.

Part	Year	Title	Core Content
PD CEN/TS 16835-1	2015	Isolated cellular RNA	Pre-examination requirements for venous whole blood used in cellular RNA analysis
PD CEN/TS 16835-2	2015	Isolated genomic DNA	Pre-examination requirements for venous whole blood used in genomic DNA analysis
PD CEN/TS 16835-3	2015	Isolated circulating cell-free DNA from plasma	Pre-examination requirements for extracting cell-free DNA from plasma

⚠️ A CEN/TS is a provisional Technical Specification, evaluated after its validity period for possible conversion into an EN. Always reference the current effective version of PD CEN TS 16835 and monitor amendments or re-issue to keep pre-examination aligned with the latest regulation and quality requirements.

2. General Considerations for Pre-examination 🧭

The general-considerations clauses identify common factors affecting the molecular quality of blood samples, spanning blood collection, anticoagulation, transport, separation, storage, and extraction:

Collection and anticoagulation: the anticoagulant in the collection tube (EDTA, citrate, etc.) affects cell integrity and nucleic-acid stability.
Transport and storage: time and temperature from collection to processing are key to minimising molecular changes.
Blood component separation: the timing and centrifugation conditions for separating plasma from cellular components affect cfDNA and cellular nucleic-acid quality.
Extraction and quantitation: extraction methods should be standardised, with nucleic-acid yield, purity, and integrity assessed.

The general considerations also stress quality control and record-keeping so that the pre-examination of every blood sample is traceable and repeatable.

3. Cellular RNA Analysis: Part 1 Requirements 🧪

Part 1 specifies pre-examination requirements for venous whole blood used for isolated cellular RNA analysis. The gene-expression profile of blood cells changes rapidly after collection, so rapid stabilisation (e.g., addition of an RNA stabiliser) and controlled processing time are needed.

Key Step	Requirement
Sample stabilisation	Add an RNA stabiliser or refrigerate promptly after collection to suppress gene-expression changes
RNA extraction	Standardise methods, avoiding RNA degradation and genomic DNA contamination
Integrity assessment	Evaluate RNA integrity via RIN or similar metrics
Applications	Whole-blood gene-expression analysis, infection and immune-response studies, etc.

4. Genomic DNA Analysis: Part 2 Requirements 🧬

Part 2 specifies pre-examination requirements for venous whole blood used for isolated genomic DNA analysis. Leucocytes are the main source of genomic DNA, so haemolysis and cell lysis causing degradation must be avoided.

Key Step	Requirement
Anticoagulation and storage	Choose an appropriate anticoagulant and control storage conditions to prevent DNA degradation
DNA extraction	Standardise extraction methods, assess purity and high-molecular-weight integrity
Degradation assessment	Evaluate DNA quality by electrophoresis or quantitation to support downstream PCR/sequencing
Applications	Hereditary-disease gene testing, pharmacogenomics, parentage testing, etc.

5. Plasma Cell-Free DNA Analysis: Part 3 Requirements 🧫

Part 3 specifies pre-examination requirements for extracting cell-free DNA (cfDNA) from plasma of venous whole blood. cfDNA is low in abundance and easily degraded, imposing the strictest requirements on post-collection timing, centrifugation, and plasma separation.

Key Step	Requirement
Plasma separation	Standardise centrifugation, avoid leucocyte contamination and haemolysis, and separate plasma promptly
cfDNA extraction	Use dedicated methods, controlling cfDNA yield and purity
Contamination control	Avoid genomic DNA interference to preserve cfDNA assay specificity
Applications	Liquid biopsy, tumour mutation detection, non-invasive prenatal testing (NIPT), etc.

✅ The three parts form a complete pre-examination specification for venous whole blood: cellular RNA focuses on ex-vivo stabilisation, genomic DNA on anticoagulation and degradation control, and plasma cfDNA on separation timing and low-abundance detection — together ensuring reliable, repeatable downstream molecular assays.

6. Engineering Practice and Application Notes 🛠️

🔍 End-to-end sample management: every step from collection, transport, separation to extraction should follow standard operating procedures (SOPs) with records for traceability.
🔧 Quality-control indicators: use nucleic-acid integrity, purity, cfDNA concentration, and fragment distribution as release criteria; re-test or re-sample non-conforming specimens.
📊 Alignment with liquid-biopsy assays: pre-examination specifications should pair with downstream methods (NGS, qPCR, ddPCR) to form a whole-chain quality system.
📋 Regulatory compliance: IVD-related requirements should be aligned with the EU IVDR and UK regulations, accounting for the impact of pre-examination on clinical results.

7. Frequently Asked Questions ❓

❓ Q: Why is pre-examination so critical for blood samples?
A: After collection, blood cell activity and nucleic-acid state change quickly — RNA expression drifts and cfDNA degrades within hours. The more standardised the pre-examination, the more reliable the downstream results.

❓ Q: How does processing differ for cellular RNA versus plasma cfDNA?
A: Cellular RNA needs rapid stabilisation and suppression of expression change; plasma cfDNA needs prompt plasma separation, controlled centrifugation, and avoidance of leucocyte contamination. Separation strategies and time windows differ.

❓ Q: What is the impact of anticoagulant choice?
A: Different anticoagulants (e.g., EDTA, citrate, heparin) affect cell integrity and nucleic-acid stability differently, and some interfere with downstream PCR; choose according to the analyte.

🔍 Q: Why is this series published as PD rather than an EN?
A: Because it is the UK implementation of a CEN/TS technical specification of provisional application, subject to evaluation before promotion; BSI adopts and publishes it as a Published Document.

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